Solid-state imaging device, method for driving the same, method for manufacturing the same, camera, and method for driving the same

ABSTRACT

A solid-state imaging device includes a two-dimensional array of photosensor sections on a semiconductor substrate, and a vertical transfer section including two-layer vertical transfer electrodes. The photosensor sections store signal charges generated by photoelectric conversion. The vertical transfer section reads signal charges from the photosensor sections and vertically transfers the read signal charges. The two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, and the first transfer electrode layers serve as read electrodes for reading the signal charges from the photosensor sections. The first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2004-226264 filed in the Japanese Patent Office on Aug.3, 2004, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device used inapparatuses such as cameras, a method for driving the solid-stateimaging device, and a method for manufacturing the solid-state imagingdevice. The present invention further relates to a camera including thesolid-state imaging device and a method for driving the camera.

2. Description of the Related Art

In the related art, image sensors and digital cameras includecharge-coupled-device (CCD) solid-state imaging devices of the interlinetransfer type. A CCD solid-state imaging device includes atwo-dimensional array of photosensor sections and a plurality ofvertical transfer registers (vertical CCDs) disposed at every column ofthe photosensor sections. The photosensor sections and the verticaltransfer registers constitute an imaging area. The CCD solid-stateimaging device further includes a horizontal transfer register(horizontal CCD) and an output section outside the imaging area. In aCCD solid-state imaging device, for example, a CCD solid-state imagingdevice used in video equipment with a large screen, such as asolid-state imaging device with high output rate used in ahigh-definition television (HDTV) system, it is necessary to drive thevertical transfer registers at a high rate. It is therefore common tosupply clock signals to the vertical transfer registers usinglow-resistance shunt lines (see, for example, Japanese Unexamined PatentApplication Publication No. 6-268192).

FIGS. 5A and 5B show the structure of a CCD solid-state imaging deviceof the related art having shunt lines. FIG. 5A is a plan view of the CCDsolid-state imaging device, showing the main portion thereof, and FIG.5B is a cross-sectional view of the CCD solid-state imaging device,taken along a line VB-VB of FIG. 5A. While one photosensor section 51 ona surface of a semiconductor substrate (not shown) is shown in FIGS. 5Aand 5B, a plurality of photosensor sections 51 is arranged in atwo-dimensional array on the semiconductor substrate. The semiconductorsubstrate has two-layer vertical transfer electrodes formed thereon witha gate insulator film 52 interposed. Each of the vertical transferelectrodes includes a first transfer electrode layer 53 and a secondtransfer electrode layer 54.

Shunt lines 55 are formed in the first transfer electrode layers 53 andthe second transfer electrode layers 54. The shunt lines 55 are made ofa low-resistance material, and they are formed in the verticaldirection. One of two horizontally adjacent shunt lines 55 includescontact sections 56 electrically connecting this shunt line 55 and thefirst transfer electrode layers 53, and the other shunt line 55 includescontact sections 57 electrically connecting the other shunt line 55 andthe second transfer electrode layers 54. Each of the photosensorsections 51 is a photodiode PD having a PN junction in which a p⁺-typesemiconductor region and an n-type semiconductor region are combined,and the photodiodes PD are separated by channel stops CS.

In the above-described configuration, vertical transfer registers aredriven by four-phase driving pulses, and driving pulses Vφ1, Vφ2, Vφ3,and Vφ4 shown in FIG. 5A are individually applied to the verticallyadjacent first and second transfer electrode layers 53 and 54 via thecorresponding shunt lines 55 and the contact sections 56 and 57. In therelated art, the driving pulses Vφ1, Vφ2, Vφ3, and Vφ4 are appliedaccording to a waveform shown in FIG. 6 so that the second transferelectrode layers 54 read signal charges stored in the photosensorsections 51. In order to reduce a read voltage to be applied to thesecond transfer electrode layers 54, an electrode width (or readoutelectrode width) W2 of the second transfer electrode layers 54 is aslarge as an electrode width W1 of the first transfer electrode layers 53with respect to the photosensor sections 51.

SUMMARY OF THE INVENTION

Recently, the pixel size has been reduced with an increase in the numberof pixels per unit area. The larger the electrode width W2 of the secondtransfer electrode layers 54, the smaller with respect to thephotosensor sections 51 the electrode width W1 of the first transferelectrode layers 53, resulting in a smaller space for the contactsections 56. Thus, hole processing for the contact sections 56 isdifficult, and the contact resistance increases, which may causedegradation in vertical transfer efficiency. Conversely, as shown inFIG. 7, the larger the electrode width W1 of the first transferelectrode layers 53, the smaller the electrode width W2 of the secondtransfer electrode layers 54, leading to a high read voltage to beapplied to the second transfer electrode layers 54 for reading thesignal charges from the photosensor sections 51. In addition, allnecessary signal charges may not be read.

According to an embodiment of the present invention, there is provided asolid-state imaging device including the following elements. Atwo-dimensional array of photosensor sections on a semiconductorsubstrate stores signal charges generated by photoelectric conversion.Vertical transfer means including two-layer vertical transfer electrodesreads signal charges from the photosensor sections and verticallytransfers the read signal charges. The two-layer vertical transferelectrodes have first transfer electrode layers and second transferelectrode layers, and the first transfer electrode layers serve as readelectrodes for reading the signal charges from the photosensor sections.The electrode width of the first transfer electrode layers is largerthan the electrode width of the second transfer electrode layers withrespect to the photosensor sections.

According to another embodiment of the present invention, there isprovided a camera including the above-described solid-state imagingdevice and a lens disposed in front of the photosensor sections of thesolid-state imaging device.

In the solid-state imaging device and the camera according to anembodiment of the present invention, the first transfer electrode layersserve as read electrodes for reading the signal charges from thephotosensor sections, and the electrode width of the first transferelectrode layers is larger than that of the second transfer electrodelayers with respect to the photosensor sections. Thus, when the shuntlines are formed on the vertical transfer electrodes, a large readelectrode width for reading signal charges from the photosensor sectionsand a large structural space for the contacts connecting the firsttransfer electrode layers and the shunt lines can be maintained.

With a large electrode width of the read electrodes for reading signalcharges from the photosensor sections and a large space for thecontacts, the solid-state imaging device and the camera according to anembodiment of the present invention can address the reduction in pixelsize.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a CCD solid-state imaging device, towhich an embodiment of the present invention is applied;

FIG. 2A is a plan view of a solid-state imaging device according to anembodiment of the present invention;

FIG. 2B is a cross-sectional view of the solid-state imaging device,taken along a line IIB-IIB of FIG. 2A;

FIG. 3A is a plan view of the solid-state imaging device having a lightshielding film;

FIGS. 3B and 3C are cross-sectional views of the solid-state imagingdevice, taken along lines IIIB-IIIB and IIIC-IIIC of FIG. 3A,respectively;

FIG. 4 is a waveform of driving pulses for vertical transfer accordingto an embodiment of the present invention;

FIG. 5A is a plan view of a CCD solid-state imaging device of therelated art;

FIG. 5B is a cross-sectional view of the CCD solid-state imaging deviceof the related art, taken along a line VB-VB of FIG. 5A;

FIG. 6 is a waveform of driving pulses for vertical transfer in therelated art;

FIG. 7 is a diagram of another CCD solid-state imaging device of therelated art; and

FIG. 8 is a schematic diagram of a camera according to an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Specific embodiments of the present invention will be described indetail hereinafter with reference to the drawings.

FIG. 1 schematically shows a CCD solid-state imaging device, to which anembodiment of the present invention is applied. In FIG. 1, atwo-dimensional array of photosensor sections 1 is arranged in animaging area of the CCD solid-state imaging device. Each of thephotosensor sections 1 has a photoelectric conversion function forgenerating a signal charge according to the amount of incident light anda charge storage function for storing the signal charge generated byphotoelectric conversion. In the imaging area, a plurality of verticaltransfer registers 2 also are disposed along the vertical axis withrespect to the photosensor sections 1. The vertical transfer registers 2have a structure in which a plurality of metal-oxide-semiconductor (MOS)capacitors (not shown) is vertically adjacent, and driving pulses areindividually applied to the MOS capacitors. Each of the verticaltransfer registers 2 is disposed adjacently at every column of thephotosensor sections 1. The vertical transfer registers 2 are verticalCCDs vertically transferring the signal charges read from thecorresponding columns of the photosensor sections 1 in a sequentialmanner.

A horizontal transfer register 3 is disposed along the horizontal axisat an end of the vertical transfer registers 2. The horizontal transferregister 3 is a horizontal CCD horizontally transferring the signalcharges vertically transferred by the vertical transfer registers 2. Thesignal charges are transferred from the horizontal transfer register 3to an output amplifier 4. The output amplifier 4 converts the signalcharges transferred by the horizontal transfer register 3 into a voltageand outputs the voltage.

A plurality of pads for driving pulses Vφ1, Vφ2, Vφ3, and Vφ4 forvertical transfer, a power supply voltage V_(DD), an output signalV_(out), a ground GND, a reset gate driving pulse φRG, driving pulsesHφ1 and Hφ2 for horizontal transfer, an electronic shutter pulse φSUB,and electrostatic protection V_(L) also are disposed around the imagingarea. The driving pulses Vφ1, Vφ2, Vφ3, and Vφ4 for vertical transferare supplied to transfer electrodes (described below) of the verticaltransfer registers 2, and the driving pulses Hφ1 and Hφ2 for horizontaltransfer are supplied to a transfer electrode of the horizontal transferregister 3.

FIGS. 2A and 2B show the structure of a solid-state imaging deviceaccording to an embodiment of the present invention. FIG. 2A is a planview of the solid-state imaging device, showing the main portionthereof, and FIG. 2B is a cross-sectional view of the solid-stateimaging device, taken along a line IIB-IIB of FIG. 2A. In FIGS. 2A and2B, photosensor sections 1 are arranged in a two-dimensional array on asurface of a semiconductor substrate (not shown) formed of a P-typesilicon substrate, and they are provided for pixels in one-to-onecorrespondence in the vertical and horizontal directions. Each of thephotosensor sections 1 may be a photodiode PD having a PN junction inwhich a p⁺-type semiconductor region and a n-type semiconductor regionare combined, and the photodiodes PD are separated by channel stops CS.

A method for manufacturing a solid-state imaging device and a cameraaccording to an embodiment of the present invention now will bedescribed.

A method for manufacturing a solid-state imaging device according to anembodiment of the present invention includes the steps of forming atwo-dimensional array of photosensor sections on a semiconductorsubstrate and forming vertical transfer means including two-layervertical transfer electrodes for reading signal charges from thephotosensor sections and vertically transferring the read signalcharges. The two-layer vertical transfer electrodes have first transferelectrode layers and second transfer electrode layers, and the firsttransfer electrode layers serve as read electrodes for reading thesignal charges from the photosensor sections. The electrode width of thefirst transfer electrode layers is larger than that of the secondtransfer electrode layers with respect to the photosensor sections.

A method for manufacturing a camera according to an embodiment of thepresent invention further includes a step of forming a lens in front ofthe photosensor sections of the solid-state imaging device in additionto the steps described above.

The vertical transfer electrodes have shunt lines formed thereon. Eachof the shunt lines is made of a material having a lower sheet resistancethan polycrystalline silicon. The first transfer electrode layers andthe second transfer electrode layers are shifted with respect to eachother in the vertical direction between the photosensor sections thatare vertically adjacent. The shunt lines are formed one-by-one betweenthe photosensor sections that are arranged in the horizontal directionwith a predetermined pitch.

A first shunt line in the shunt lines includes first contact sectionselectrically connecting the first shunt line and the first transferelectrode layers, and a second shunt line in the shunt lines includessecond contact sections electrically connecting the second shunt lineand the second transfer electrode layers. The first and second contactsections are offset by about half a pixel in the vertical direction.

The semiconductor substrate has two-layer vertical transfer electrodesformed thereon with a gate insulator film 5 interposed, e.g., silicondioxide (SiO₂). The two-layer vertical transfer electrodes correspond tothe vertical transfer registers 2 shown in FIG. 1, and they includefirst transfer electrode layers 6 and second transfer electrode layers 7formed thereafter. The transfer electrode layers 6 and 7 are made ofpolycrystalline silicon, and they are formed so as to surround thephotosensor sections 1, when viewed two-dimensionally. Each of thetransfer electrode layers 6 and 7 is coated with an insulator film.

Shunt lines 8 extend in the first transfer electrode layers 6 and thesecond transfer electrode layers 7. The shunt lines 8 are made of amaterial having a lower sheet resistance than polycrystalline silicon,such as aluminum or tungsten, and extend vertically in the verticaltransfer registers 2. The shunt lines 8 are disposed one-by-one betweenphotosensor sections 1 arranged in the horizontal direction with apredetermined pitch. One of two horizontally adjacent shunt lines 8includes contact sections 9 electrically connecting this shunt line 8and the first transfer electrode layers 6, and the other shunt line 8includes contact sections 10 electrically connecting the other shuntline 8 and the second transfer electrode layers 7. The contact sections9 and 10 are offset by about half a pixel in the vertical direction. Asshown in FIG. 1, if the vertical transfer registers 2 are driven byfour-phase driving pulses Vφ1, Vφ2, Vφ3, and Vφ4, the contact sections 9and the contact sections 10 are provided for every four pixels in thehorizontal direction.

Although not shown in FIGS. 2A and 2B, which show the fundamentalconfiguration of the solid-state imaging device, a light shielding filmis actually formed. FIGS. 3A to 3C show the structure of the solid-stateimaging device having a light shielding film 11. FIG. 3A is a plan viewof the solid-state imaging device, showing the main portion thereof,FIG. 3B is a cross-sectional view of the solid-state imaging device,taken along a line IIIB-IIIB of FIG. 3A, and FIG. 3C is across-sectional view of the solid-state imaging device, taken along aline IIIC-IIIC of FIG. 3A. The light shielding film 11 has openings fromwhich the photosensor sections 1 are exposed. In FIG. 3C, vertical CCDs12 are disposed between the photodiodes PD with the channel stops CS andread gates TG interposed. Each of the vertical CCDs 12 has a PN junctionin which a n-type semiconductor region and a p-type semiconductor regionare combined.

In an embodiment of the present invention, the first transfer electrodelayers 6 are read electrodes for reading signal charges from thephotosensor sections 1, and an electrode width W1 of the first transferelectrode layers 6 serving as read electrodes is larger than anelectrode width W2 of the second transfer electrode layers 7. Drivingpulses Vφ1, Vφ2, Vφ3, and Vφ4 for vertical transfer having a waveformshown in FIG. 4 are applied to the transfer electrode layers 6 and 7 inthe manner shown in FIG. 2A, and read pulses are supplied to the firsttransfer electrode layers 6, thereby reading signal charges from thephotosensor sections 1 to the vertical transfer registers 2.Specifically, the driving pulses Vφ1, Vφ2, Vφ3, and Vφ4 for verticaltransfer may be pulses having three levels of, for example, 15 V, 0 V,and −7 V. Among them, the pulses of 0 V and −7 V are used fortransferring signal charges and the pulses of 15 V are used for readingsignal charges. The driving pulses V+2 and V+4 to be applied to thefirst transfer electrode layers 6 that are vertically adjacent becomeread pulses of 15 V at individual predetermined timings, and signalcharges are read from the photosensor sections 1 to the verticaltransfer registers 2 in response to these read pulses.

The electrode width W1 of the first transfer electrode layers 6represents the electrode length in the vertical direction of the firsttransfer electrode layers 6 contacted with the gate oxide film 5 in aportion adjacent to the photosensor sections 1. The electrode width W2of the second transfer electrode layers 7 represents the electrodelength in the vertical direction of the second transfer electrode layers7 contacted with the gate oxide film 5 in a portion adjacent to thephotosensor sections 1. Since the second transfer electrode layers 7 arestacked on the first transfer electrode layers 6, a portion of thesecond transfer electrode layers 7 which overlaps the first transferelectrode layers 6 is not contacted with the gate oxide film 5.

FIG. 8 is a schematic block diagram of a camera 60 including theabove-described solid-state imaging device.

The camera 60 includes a solid-state imaging device (CCD) 61, an opticalsystem 62, a driving circuit 63, and a signal processing circuit 64.

The optical system 62 focuses image light (or incident light) reflectedfrom an object onto an imaging surface of the solid-state imaging device61. In the solid-state imaging device 61, the photosensor sections 1convert the incident light into signal charges according to the amountof incident light and store the signal charges in signal charge storageregions of the photosensor sections 1 for a certain period of time.

The driving circuit 63 supplies timing signals, e.g., theabove-described four-phase clock signals Vφ1, Vφ2, Vφ3, and Vφ4 andtwo-phase clock signals Hφ1 and Hφ2, to the solid-state imaging device61. In response to these timing signals, the solid-state imaging device61 is driven to read, vertically transfer, and horizontally transfer thesignal charges. Then, an analog image signal is output from an outputunit of the solid-state imaging device 61.

The signal processing circuit 64 performs signal processing, such asnoise rejection and conversion into a digital signal, on the analogsignal output from the solid-state imaging device 61. The signalsubjected to signal processing by the signal processing circuit 64 isstored in a storage medium, such as a memory.

Since the solid-state imaging device 61, which provides a low readvoltage, is used in the camera 60, e.g., a video camera or a digitalstill camera, the camera 60 can provide low power consumption.

With the above-described electrode structure, the electrode width forreading signal charges from the photosensor sections 1 corresponds tothe electrode width W1 of the first transfer electrode layers 6, whereinthe electrode width W1 is relatively larger than the electrode width W2of the second transfer electrode layers 7. Thus, the voltage of readpulses to be applied for reading the signal charges can be reduced.Moreover, a large space for the contact sections 9 electricallyconnecting the first transfer electrode layers 6 and the shunt lines 8facilitates hole processing for the contact sections 9, while reducingthe contact resistance. The electrode structure described above cantherefore address the reduction in pixel size.

In a region defined by the vertically adjacent photosensor sections 1,the second transfer electrode layers 7 are formed on the first transferelectrode layers 6 so that the first transfer electrode layers 6 and thesecond transfer electrode layers 7 are shifted with respect to eachother in the vertical direction, and a portion of the second transferelectrode layers 7 is contacted with the gate oxide film 5. Thus, theelectrode width (cross-section area) of the second transfer electrodelayers 7 between the photosensor sections 1 in the vertical direction islarge, and the electrode resistance is reduced. In this structure, asshown in the waveform shown in FIG. 4, when a positive read pulse isapplied to the first transfer electrode layers 6, a pulse of 0 V or apulse of negative voltage is applied to the second transfer electrodelayers 7. A potential barrier between the photosensor sections 1 in thevertical direction can prevent the mixture of the signal charges (colormixture) between the pixels in the vertical direction.

It should be understood by those skilled in the art that variousmodifications, combinations, subcombinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A solid-state imaging device comprising: a two-dimensional array of photosensor sections on a semiconductor substrate for storing signal charges generated by photoelectric conversion; and vertical transfer means including two-layer vertical transfer electrodes for reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, the first transfer electrode layers serve as read electrodes for reading the signal charges from the photosensor sections, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers.
 2. The solid-state imaging device according to claim 1, wherein the two-layer vertical transfer electrodes include shunt lines.
 3. The solid-state imaging device according to claim 2, wherein each of the shunt lines is made of a material having a lower sheet resistance than polycrystalline silicon.
 4. The solid-state imaging device according to claim 2, wherein the shunt lines are formed one-by-one between the photosensor sections that are arranged in the horizontal direction with a predetermined pitch.
 5. The solid-state imaging device according to claim 2, wherein a first shunt line in the shunt lines includes first contact sections electrically connecting the first shunt line and the first transfer electrode layers, and a second shunt line in the shunt lines includes second contact sections electrically connecting the second shunt line and the second transfer electrode layers, the first contact sections and the second contact sections being offset by about half a pixel in the vertical direction.
 6. The solid-state imaging device according to claim 1, wherein the first transfer electrode layers and the second transfer electrode layers are shifted with respect to each other in the vertical direction between the photosensor sections that are vertically adjacent.
 7. A method for driving a solid-state imaging device including a two-dimensional array of photosensor sections on a semiconductor substrate for storing signal charges generated by photoelectric conversion, and vertical transfer means including two-layer vertical transfer electrodes for reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers, the method comprising a step of reading signal charges from the photosensor sections by applying read pulses to the first transfer electrode layers.
 8. A camera comprising: a solid-state imaging device including a two-dimensional array of photosensor sections on a semiconductor substrate for storing signal charges generated by photoelectric conversion, and vertical transfer means including two-layer vertical transfer electrodes for reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, the first transfer electrode layers serve as read electrodes for reading the signal charges from the photosensor sections, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers; and a lens disposed in front of the photosensor sections of the solid-state imaging device.
 9. The camera according to claim 8, wherein the vertical transfer electrodes include shunt lines.
 10. The camera according to claim 9, wherein each of the shunt lines is made of a material having a lower sheet resistance than polycrystalline silicon.
 11. The camera according to claim 9, wherein the shunt lines are formed one-by-one between the photosensor sections that are arranged in the horizontal direction with a predetermined pitch.
 12. The camera according to claim 9, wherein a first shunt line in the shunt lines includes first contact sections electrically connecting the first shunt line and the first transfer electrode layers, and a second shunt line in the shunt lines includes second contact sections electrically connecting the second shunt line and the second transfer electrode layers, the first contact sections and the second contact sections being offset by about half a pixel in the vertical direction.
 13. The camera according to claim 8, wherein the first transfer electrode layers and the second transfer electrode layers are shifted with respect to each other in the vertical direction between the photosensor sections that are vertically adjacent.
 14. A method for driving a camera including a solid-state imaging device, the solid-state imaging device including a two-dimensional array of photosensor sections on a semiconductor substrate for storing signal charges generated by photoelectric conversion, vertical transfer means including two-layer vertical transfer electrodes for reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers, the method comprising a step of reading signal charges from the photosensor sections by applying read pulses to the first transfer electrode layer when driving the solid-state imaging device.
 15. A solid-state imaging device comprising: a two-dimensional array of photosensor sections on a semiconductor substrate storing signal charges generated by photoelectric conversion; and a vertical transfer section including two-layer vertical transfer electrodes reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, the first transfer electrode layers serve as read electrodes for reading the signal charges from the photosensor sections, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers.
 16. A camera comprising: a solid-state imaging device including a two-dimensional array of photosensor sections on a semiconductor substrate storing signal charges generated by photoelectric conversion, and a vertical transfer section including two-layer vertical transfer electrodes reading signal charges from the photosensor sections and vertically transferring the read signal charges, wherein the two-layer vertical transfer electrodes have first transfer electrode layers and second transfer electrode layers, the first transfer electrode layers serve as read electrodes for reading the signal charges from the photosensor sections, and the first transfer electrode layers have a larger electrode width with respect to the photosensor sections than the second transfer electrode layers; and a lens disposed in front of the photosensor sections of the solid-state imaging device. 